<?php

namespace Aws\Api;

use Aws\Exception\UnresolvedApiException;

/**
 * API providers.
 *
 * An API provider is a function that accepts a type, service, and version and
 * returns an array of API data on success or NULL if no API data can be created
 * for the provided arguments.
 *
 * You can wrap your calls to an API provider with the
 * {@see ApiProvider::resolve} method to ensure that API data is created. If the
 * API data is not created, then the resolve() method will throw a
 * {@see Aws\Exception\UnresolvedApiException}.
 *
 *     use Aws\Api\ApiProvider;
 *     $provider = ApiProvider::defaultProvider();
 *     // Returns an array or NULL.
 *     $data = $provider('api', 's3', '2006-03-01');
 *     // Returns an array or throws.
 *     $data = ApiProvider::resolve($provider, 'api', 'elasticfood', '2020-01-01');
 *
 * You can compose multiple providers into a single provider using
 * {@see Aws\or_chain}. This method accepts providers as arguments and
 * returns a new function that will invoke each provider until a non-null value
 * is returned.
 *
 *     $a = ApiProvider::filesystem(sys_get_temp_dir() . '/aws-beta-models');
 *     $b = ApiProvider::manifest();
 *
 *     $c = \Aws\or_chain($a, $b);
 *     $data = $c('api', 'betaservice', '2015-08-08'); // $a handles this.
 *     $data = $c('api', 's3', '2006-03-01');          // $b handles this.
 *     $data = $c('api', 'invalid', '2014-12-15');     // Neither handles this.
 */
class ApiProvider {
	/** @var array A map of public API type names to their file suffix. */
	private static $typeMap = [
		'api' => 'api-2',
		'paginator' => 'paginators-1',
		'waiter' => 'waiters-2',
		'docs' => 'docs-2',
	];

	/** @var array API manifest */
	private $manifest;

	/** @var string The directory containing service models. */
	private $modelsDir;

	/**
	 * Resolves an API provider and ensures a non-null return value.
	 *
	 * @param callable $provider Provider function to invoke.
	 * @param string $type Type of data ('api', 'waiter', 'paginator').
	 * @param string $service Service name.
	 * @param string $version API version.
	 *
	 * @return array
	 * @throws UnresolvedApiException
	 */
	public static function resolve(callable $provider, $type, $service, $version) {
		// Execute the provider and return the result, if there is one.
		$result = $provider($type, $service, $version);
		if(is_array($result)) {
			if(!isset($result['metadata']['serviceIdentifier'])) {
				$result['metadata']['serviceIdentifier'] = $service;
			}
			return $result;
		}

		// Throw an exception with a message depending on the inputs.
		if(!isset(self::$typeMap[$type])) {
			$msg = "The type must be one of: ".implode(', ', self::$typeMap);
		} elseif($service) {
			$msg = "The {$service} service does not have version: {$version}.";
		} else {
			$msg = "You must specify a service name to retrieve its API data.";
		}

		throw new UnresolvedApiException($msg);
	}

	/**
	 * Default SDK API provider.
	 *
	 * This provider loads pre-built manifest data from the `data` directory.
	 *
	 * @return self
	 */
	public static function defaultProvider() {
		return new self(__DIR__.'/../data', \Aws\manifest());
	}

	/**
	 * Loads API data after resolving the version to the latest, compatible,
	 * available version based on the provided manifest data.
	 *
	 * Manifest data is essentially an associative array of service names to
	 * associative arrays of API version aliases.
	 *
	 * [
	 *   ...
	 *   'ec2' => [
	 *     'latest'     => '2014-10-01',
	 *     '2014-10-01' => '2014-10-01',
	 *     '2014-09-01' => '2014-10-01',
	 *     '2014-06-15' => '2014-10-01',
	 *     ...
	 *   ],
	 *   'ecs' => [...],
	 *   'elasticache' => [...],
	 *   ...
	 * ]
	 *
	 * @param string $dir Directory containing service models.
	 * @param array $manifest The API version manifest data.
	 *
	 * @return self
	 */
	public static function manifest($dir, array $manifest) {
		return new self($dir, $manifest);
	}

	/**
	 * Loads API data from the specified directory.
	 *
	 * If "latest" is specified as the version, this provider must glob the
	 * directory to find which is the latest available version.
	 *
	 * @param string $dir Directory containing service models.
	 *
	 * @return self
	 * @throws \InvalidArgumentException if the provided `$dir` is invalid.
	 */
	public static function filesystem($dir) {
		return new self($dir);
	}

	/**
	 * Retrieves a list of valid versions for the specified service.
	 *
	 * @param string $service Service name
	 *
	 * @return array
	 */
	public function getVersions($service) {
		if(!isset($this->manifest)) {
			$this->buildVersionsList($service);
		}

		if(!isset($this->manifest[$service]['versions'])) {
			return [];
		}

		return array_values(array_unique($this->manifest[$service]['versions']));
	}

	/**
	 * Execute the provider.
	 *
	 * @param string $type Type of data ('api', 'waiter', 'paginator').
	 * @param string $service Service name.
	 * @param string $version API version.
	 *
	 * @return array|null
	 */
	public function __invoke($type, $service, $version) {
		// Resolve the type or return null.
		if(isset(self::$typeMap[$type])) {
			$type = self::$typeMap[$type];
		} else {
			return null;
		}

		// Resolve the version or return null.
		if(!isset($this->manifest)) {
			$this->buildVersionsList($service);
		}

		if(!isset($this->manifest[$service]['versions'][$version])) {
			return null;
		}

		$version = $this->manifest[$service]['versions'][$version];
		$path = "{$this->modelsDir}/{$service}/{$version}/{$type}.json";

		try {
			return \Aws\load_compiled_json($path);
		} catch (\InvalidArgumentException $e) {
			return null;
		}
	}

	/**
	 * @param string $modelsDir Directory containing service models.
	 * @param array $manifest The API version manifest data.
	 */
	private function __construct($modelsDir, array $manifest = null) {
		$this->manifest = $manifest;
		$this->modelsDir = rtrim($modelsDir, '/');
		if(!is_dir($this->modelsDir)) {
			throw new \InvalidArgumentException(
				"The specified models directory, {$modelsDir}, was not found."
			);
		}
	}

	/**
	 * Build the versions list for the specified service by globbing the dir.
	 */
	private function buildVersionsList($service) {
		$dir = "{$this->modelsDir}/{$service}/";

		if(!is_dir($dir)) {
			return;
		}

		// Get versions, remove . and .., and sort in descending order.
		$results = array_diff(scandir($dir, SCANDIR_SORT_DESCENDING), ['..', '.']);

		if(!$results) {
			$this->manifest[$service] = ['versions' => []];
		} else {
			$this->manifest[$service] = [
				'versions' => [
					'latest' => $results[0]
				]
			];
			$this->manifest[$service]['versions'] += array_combine($results, $results);
		}
	}
}
